CATION-SPECIFIC ELECTRODES - VARIATION OF ELECTRICAL-PROPERTIES OF THE MEMBRANE AS FUNCTION OF ITS COMPOSITION

Amphiphilic-cation-specific electrodes most often use, as captor of potential, a specific membrane composed of a mixture of a polymer such as PVC, a plasticizer, and a carrier of the amphiphilic ion. For a given polymer, various plasticizers can be used to make ''plastisols'' that can be suitable for the preparation of specific membranes. We prepared different membranes using two polymers (PVC: high and low molecular weight), four plasticizers in various proportions, and a carrier of the dodecyltrimethylammonium ion. These membranes were mounted on an electrode support and used as ion-selective electrodes. We show that none of these component mixtures can allow the design of specific electrodes. Only a few of them give a ''Nernstian'' response. Thus, the mixtures rich in polymer lead to heterogeneous plastisols; the electrode responses cannot be reproduced with different samples of the same mixture. We use a model of ion transport through the membrane that assumes a diffusion by carrier for the amphiphilic ion and nonspecific diffusion of the salt through the flaws created by the heterogeneity of the plastisols. The introduction of this model allows us to explain qualitatively the variation of the slope of the electrode response with the membrane composition.